Pressure swing adsorption (PSA) processes are widely used for the separation of gas mixtures based upon cyclic adsorption-desorption steps utilizing one or more vessels containing selective adsorbents that effect the desired separation. A PSA system typically comprises adsorbent vessels, compressors, vacuum pumps, multiple valves, piping, gas storage tanks, and a control system to operate the valves to provide the required cyclic process steps. Significant portions of the capital cost and operating maintenance expenses of PSA systems may be attributed to the multiple valves and control system required to operate these valves for the multiple cyclic steps in a PSA process.
PSA systems are competitive with cryogenic distillation systems for separating air to produce oxygen at capacities up to about 100 tons per day (TPD). Capital costs must be controlled and reduced for these PSA systems to remain competitive in view of changing market needs and increasing energy costs. As a result of recent improvements in adsorbent technology, oxygen PSA systems can be reduced in size and complexity to become transportable, and systems with product capacities up to 1 TPD can be transported easily on skids and commissioned at customer sites in minimal time. The modularization of these small PSA systems requires the reduction in component complexity, improved reliability, and lower capital cost.
There is a need in the art to simplify the valves and control systems in PSA systems, particularly in small modularized systems, in order to meet these requirements. This need is addressed by the embodiments of the invention disclosed below and defined by the claims that follow.